The chemical truck did not have a pump, but rather functioned much like a gigantic soda ash fire extinguisher. Acid, mixed with an alkaline water, would generate carbon dioxide (CO2), creating pressure within the tank that would be used to pressurize the hose. Once the water was expelled, the truck would need to be refilled and the process repeated. By today's standards it was inefficient; similar fire extinguishers are no longer in use.

Unfortunately, I've had considerably less luck finding a photograph of a unit similar to the one purchased by Columbia in 1921. Jim